Alumina ceramic material is famous for use as a cutting tool material and has high abrasion resistance, but has certain disadvantages. Therefore, the improvement of toughness is a major object of the development of the alumina.
That zirconia phases are finely dispersed in the alumina matrix so that the finely dispersed tetragonal zirconia will transfer to the monoclinic phase under stress and crack, and therefore the energy of crack in the alumina ceramics will be absorbed. When the zirconia phase does not contain a stabilizing agent, zirconia particles will maintain the tetragonal phase and be stable in the alumina matrix. The size of the particle needs to be less than the critical size (in order of 0.5 .mu.m). However, such fine dispersion can not be produced in a commercial size for the production of the ceramic body. One was proposed in Japanese Patent Laid Open Gazette No. 54-25908 for the production of so fine dispersion wherein partially stabilized zirconia is added to the ceramic formulation so as to maintain the tetragonal phase even when the size of zirconia is more than the critical particle size.
In order to yield high density ceramics with a fine dispersion of zirconia in the ceramics, the higher temperature sintering such as at the temperature higher than 1500.degree. C. under the atmospheric pressure, ordinarily the sintering temperature of higher than 1600.degree. C. is necessary. When the lower sintering temperature is used for producing the high density ceramics, thehigher pressure for sintering should be applied (HIP treatment). However, the sintering under higher pressure is not preferable and further, when the ceramics is sintered at the higher temperature under the atmospheric pressure, the grain growth of alumina and the grain growth of zirconia together with the transformation of the crystal to monoclinic phase may easily occur so as to decrease the strength with zirconia.
In accordance with the present invention, the sintering ability of the ceramics is improved by the combination of alumina phase and zirconia phase, so that the graing rowth of alumina and zirconia would be suppressed to result in a high density alumina zirconia ceramics with high breaking toughness and high abrasion resistance.
The inventive alumina zirconia ceramics is a functional ceramics having high strength and high tenacity, and it is expected to use for structural material such as mechanical material, abrasion resistant material, and cutting material and etc..